A study of clinical variables in multiplex families with schizophrenia was completed. In 53 of these families at least 2 siblings satisfied Research Diagnostic Criteria (RDC) for schizophrenia. Brain imaging study: preliminary analysis of Magnetic Resonance Imaging (MRI) scans of these siblings revealed significantly reduced hippocampal area in schizophrenics as compared with related controls, suggesting that this may be a familial vulnerability factor. Genetic marker studies: no association of Restriction Fragment Length Polymorphisms were found in genomic DNA from schizophrenics using several neuropeptide probes and probes for chromosome 11 (see Z01 MH 02237-03 CNG). Protein polymorphisms in CSF were examined in 14 unrelated schizophrenics with a family history of schizophrenia. No abnormalities were found.